The present invention relates generally to a printed circuit board test system having a removable test fixture assembly and more particularly to a mechanical pull-down system which locates and retains the test fixture in precise electrical and mechanical contact with the main body of the printed circuit board test system. The invention further relates to connectors for interconnecting the test fixture assembly with a driver/receiver circuit board in the main body of the test system.
Today, integrated circuits are complex electronic devices, such as complete microprocessors in single integrated circuit packages. Switching speeds of digital integrated circuits have increased and frequency bandwidths of analog integrated circuits have increased. Printed circuit board design uses these advances in integrated circuit technology. Consequently, a printed circuit board may be a very complex component to test.
To test fast, complex electronic printed circuit boards, a test system must be capable of sending input stimuli to a large number of test nodes on a printed circuit board under test. The test system must be capable of accurately monitoring the responses received from the input stimuli at a sufficient number of strategic locations on the printed circuit board under test. The speed of data transmission to and from the printed circuit board should be at least as fast as the highest speed at which the printed circuit board is designed to operate, and the quality of data transmission should involve a minimum of distortion to a data signal.
To communicate with large numbers of test nodes, a printed circuit board test system requires a large number of interconnecting leads, insulated conductors, to transmit data between a number of driver/receiver boards and the test nodes on the printed circuit to be tested. To satisfy the high speed requirements in a printed circuit board test system, the interconnecting leads should be as short as practically possible.
A printed circuit board test system generally has two main parts: a main frame, or cabinet, and a test fixture assembly. The cabinet contains a number of driver/receiver boards under the control of a microprocessor and associated software. The test fixture assembly contains interconnecting leads which connect the driver/receiver boards to the test nodes on the printed circuit board to be tested. The test fixture assembly is removable from the cabinet since a test fixture assembly is unique to each particular printed circuit board layout being tested.
In the past, when less stringent performance was required, the interconnecting leads were fed through the test fixture assembly. This design left the underside of the test fixture assembly clean to make a vacuum seal, enabling a vacuum means to pull down the test fixture onto the main test assembly. The vacuum technique was convenient and relatively inexpensive. However, testing large scale integrated circuit technology (LSI) requires many more driver/receiver boards and thus more interconnecting leads. The interconnecting leads are attached to the underside of the test fixture assembly in order to keep them as short as possible. Since the underside of such a test fixture assembly is not clear because of the interconnecting leads and terminals protruding from the surface, vacuum pull-down techniques are unsuitable.
Thus, a need has existed for a reliable means to pull down a test fixture assembly onto the main test assembly. A need has also existed for such a pull-down means to allow quick and easy interchanges of test fixture assemblies, and to allow quick and easy interchanges of printed circuit boards being tested. Finally, a need has existed to shorten the interconnecting leads.
A printed circuit board test system according to the present invention has a cabinet containing a plurality of driver/receiver printed circuit boards. A platen rigidly attached to the cabinet locates and supports a plurality of driver/receiver connectors. Each driver/receiver connector makes electrical connection with an associated driver/receiver printed circuit board which, in turn, plugs into either side of a back plane. The back plane is rigidly supported in the center of the cabinet. With all the driver/receiver connectors plugged into their respective driver/receiver printed circuit boards, the driver/receiver connectors' upper surfaces form two terminal arrays along opposite sides of the platen.
Projecting from the platen, and protruding between and above the driver/receiver connectors' upper surfaces are a number of pull-down fingers, which are arranged to receive a test fixture assembly. Each test fixture assembly has a test fixture and fixture interface attached to either side of the text fixture. Each fixture interface contains an array of insulation displacement devices. The pull-down fingers are operable to pull down a test fixture assembly until the array of insulation displacement devices make electrical and physical contact with the terminal arrays formed by the driver/receiver connectors' upper surfaces. The test fixture of the test fixture assembly has a plurality of fixture spring-loaded pogo probe connectors protruding from its top surface. The fixture pogo probe connectors are arranged to make physical and electrical contact with a plurality of predetermined nodes on the solder side of the printed circuit board under test. The test fixture assembly also has fixture alignment pins which also protrude through and above the top surface of the test fixture assembly. The fixture alignment pins determine the precise location on the test fixture of a printed circuit board to be tested.
The fixture pogo probe connectors are wired to electrically connect predetermined nodes on the solder side of a printed circuit board under test to appropriate insulation displacement devices in the fixture interfaces. The test fixture assembly wiring is unique for each unique printed circuit board under test.
The insulation displacement devices in each fixture interface are arranged to mate with an array of driver/receiver pogo probe connectors positioned along the upper surfaces of the driver/receiver connectors. An opposite surface of the driver/receiver connector comprises a card-edge connector. Each driver/receiver probe connector has a separate internal wire or other conductive element which leads to a separate contact on the card-edge connector. The card-edge connector is a socket-type connector. In another feature of the invention, the card-edge connector is a plug-type connector.
To test a series of identical printed circuit boards, the operator places a test fixture assembly onto the pull-down fingers in their raised position, and above platen alignment pins. The pull-down fingers move away from under the test fixture assembly, allowing the test fixture assembly to fall, guided by the platen alignment pins. The pull-down fingers then move back over the test fixture assembly and pull the test fixture assembly down, causing the two arrays of insulation displacement devices to mate with the two terminal arrays formed by the driver/receiver connectors' upper surfaces.
The operator places the printed circuit board to be tested over the fixture alignment pins protruding from the top surface of the test fixture. A vacuum or other conventional means pulls down the printed circuit board to contact the fixture pogo probe connectors protruding from the surface of the test fixture. After the board has been tested, the operator releases the board, removes it from the test fixture, and places the next board to be tested on the test fixture.
To test a printed circuit board with a different layout, the operator must replace the first test fixture assembly with a second test fixture assembly which is wired for the new layout. The operator activates the pull-down fingers, which release the first test fixture assembly, rotate beneath the first test fixture assembly, and then support the first test fixture assembly in electrical isolation from the driver/receiver connectors. The operator removes the first test fixture assembly and places the second test fixture assembly onto the raised pull-down fingers and over the platen alignment pins. The pull-down fingers then operate to pull down the second test fixture assembly to cause the insulation displacement devices of the test fixture assembly to make electrical contact with the driver/receiver probe connectors.